The invention relates to electromagnetic energy, and more particularly, to an electromagnetic exposure chamber with a focal region.
The recent popularity of microwaves has led to the discovery of new uses for microwave energy, uses that require an electromagnetic exposure chamber with a relatively uniform power distribution. In some cases, it is advantageous if the material can be passed through--rather than simply placed in--the exposure chamber.
Researchers have experimented with placing a test specimen in a free-space environment between two axially-facing paraboloidal reflectors. See U.S. Pat. No. 3,281,727 to Niebuhr et al entitled "Traveling Wave High Power Simulation." At least one researcher has experimented with using a microwave source in an ellipsoidal shell. See U.S. Pat. No. 2,543,053 to Parker entitled "Radiant Energy High-Temperature Heating Apparatus" and U.S. Pat. No. 2,943,174 to Parker entitled "Radiant Energy Heating Apparatus." These early experiments used bowl-like structures that focus the microwave in multiple directions towards a single point. The problem with these bowl-like structures is that they form a focal point that acts like a single concentrated hot spot. There is poor coupling at the focal point and the energy tends to reflect and scatter. A major concern with the Niebuhr et al patent is that as the waves reflect and scatter, the free space environment cannot contain the electromagnetic energy. A major concern with the Parker patents is that as the waves reflect and scatter, they will propagate towards the source.
There is a need for an electromagnetic exposure chamber that can uniformly focus the electromagnetic energy to a region, rather than a single point, so as to provide more uniform heating. One possible approach is described in our co-assigned and co-pending U.S. patent application Ser. No. 08/813,061 now U.S. Pat. Nos. 5,998,774 and 6,087,642 . In this earlier application, which is herein incorporated by reference, we describe an elliptical structure that focuses the energy in a single plane (or direction). The structure focuses the energy to a focal region that extends from a first substantially planar surface to a second substantially planar surface. The elliptical structure can contain the microwave energy and still allow the material to pass in and out of the chamber.
The disclosed structure can be used with dielectric slabs or without dielectric slabs. In certain instances, the dielectric slabs increase the uniformity across the focal region. However, as the diameter (or width) of the material decreases, the ability to couple the energy into the material also decreases. As a result, it is more difficult to heat the material. As discussed below, it is possible to increase the coupling and, in some instances, decrease the need for the dielectric slabs.